An aviation turbine engine generally includes a so-called “hot” portion, that is situated downstream from the combustion chambers (where “upstream” and “downstream” are defined relative to the flow direction of the gas stream through the turbine engine), which hot portion comprises a high-pressure turbine and a low-pressure turbine. In known manner, the high-pressure turbine includes a high-pressure rotor shaft that drives rotation of a high-pressure compressor that is situated upstream, and the low-pressure turbine includes a low-pressure rotor shaft that drives rotation of a fan and of a low-pressure compressor.
Turbines are defined radially on the outside by respective turbine casings. A turbine casing comprises an annular main portion, which may optionally be sectorized, and it may also include secondary portions forming sealing portions, or attachment portions for a ring sector, e.g. projections, flanges, or hooks, that extend radially from an inside face of the casing towards the inside of the hot gas flow passage. Such secondary portions are subjected to higher temperatures than the main portion of the casing situated at the periphery of the passage. The secondary portions therefore need to be manufactured out of a material that is suitable for withstanding the large thermomechanical stresses to which they are subjected. Requirements in terms of mechanical strength and ability to withstand high temperatures therefore differ between the main portion of the casing and its secondary portions.
In known manner, superalloys, e.g. based on nickel, are used for parts of the turbine. In order to manufacture the above-mentioned casing as a single piece, it is generally necessary to form the annular main portion and the secondary portions out of the same material, and that can be found to be expensive since it is necessary to use the highest performance superalloy for the entire part. Specifically, those high-performance superalloys that are capable of withstanding the temperature inside the passage are generally more expensive and more difficult to work during manufacturing than are superalloys that are sufficient for forming the annular portion of the casing. Also, it is often difficult to use casting to work those high-performance superalloys that withstand the environmental conditions inside the passage.
There therefore exists a need for a manufacturing method that is inexpensive and easy to perform and that makes it possible to obtain a part comprising a plurality of portions made of different superalloys.